(361e) Catechin-Mediated Toxin Unfolding As an Antivirulence Strategy

With the rise in antibiotic resistance and the decrease in development of new antibiotic molecules, anti-virulence approaches have been proposed as alternatives or supplements to traditional antibiotics. Rather than killing pathogenic bacteria, anti-virulence strategies disable a specific virulence factor produced by the bacteria, thereby limiting the ability of the bacteria to colonize or invade the host. Toward this end, our lab investigates anti-toxin strategies. The leukotoxin (LtxA) produced by the oral bacterium, Aggregatibacter actinomycetemcomitans, specifically kills human white blood cells. This toxin has been demonstrated to be a key virulence factor for the organism, allowing the bacteria to inhibit clearance of the infection by the host immune system. Catechins, polyphenols found in tea, have been shown to inhibit the activity of LtxA against immune cells, but the mechanism by which this occurs has not been demonstrated. We hypothesized that because catechins have well-known membrane partitioning properties, that they alter host cell membrane structure, thus inhibiting the ability of the toxin to interact with the membrane. However, we found that the inhibitory activities of six catechins were enhanced when they were pre-incubated with the toxin, suggesting that they act on the protein toxin instead of the target cell membrane. Circular dichroism (CD) spectroscopy and tryptophan quenching experiments demonstrated that the catechins drastically alter the structure of the toxin, resulting in a much less structured protein. As a result of this unfolding, the toxin’s affinity for membrane cholesterol is significantly reduced, leading to a diminished interaction with the host cell membrane. These findings indicate that the anti-toxin activity of catechins results from their unfolding of the protein, which inhibits the ability of the toxin to interact with the host cell.